From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E449EC43334 for ; Fri, 22 Jul 2022 09:13:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235494AbiGVJNu (ORCPT ); Fri, 22 Jul 2022 05:13:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40924 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235464AbiGVJND (ORCPT ); Fri, 22 Jul 2022 05:13:03 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 40F3180F40; Fri, 22 Jul 2022 02:10:30 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D141161EE6; Fri, 22 Jul 2022 09:10:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D901AC341C6; Fri, 22 Jul 2022 09:10:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1658481029; bh=24ob/7h00TzVVLTobzWQ1zjvJdDqDNMmJEr8a2tT7g4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vj7FoYnFTZ2CCiaHIL9nn9bPtOKSewad4/8J86reIQtai9fF5j1w6o0y1JooZO6jq CYqmWFWHjh2iww4RIPWBlgeQlUHI94xZ0ykaU2znNo2x8Tpp2/27xGUQQtHrm1sefA 14MKQHSIiWa2rXiYjfxSKxTXa40Yq4tMzvNfKl2Q= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josh Poimboeuf , "Peter Zijlstra (Intel)" , Borislav Petkov , Thadeu Lima de Souza Cascardo Subject: [PATCH 5.18 52/70] KVM: VMX: Prevent RSB underflow before vmenter Date: Fri, 22 Jul 2022 11:07:47 +0200 Message-Id: <20220722090653.635310511@linuxfoundation.org> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220722090650.665513668@linuxfoundation.org> References: <20220722090650.665513668@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Josh Poimboeuf commit 07853adc29a058c5fd143c14e5ac528448a72ed9 upstream. On VMX, there are some balanced returns between the time the guest's SPEC_CTRL value is written, and the vmenter. Balanced returns (matched by a preceding call) are usually ok, but it's at least theoretically possible an NMI with a deep call stack could empty the RSB before one of the returns. For maximum paranoia, don't allow *any* returns (balanced or otherwise) between the SPEC_CTRL write and the vmenter. [ bp: Fix 32-bit build. ] Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov [cascardo: header conflict fixup at arch/x86/kernel/asm-offsets.c] Signed-off-by: Thadeu Lima de Souza Cascardo Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/asm-offsets.c | 6 ++++++ arch/x86/kernel/cpu/bugs.c | 4 ++-- arch/x86/kvm/vmx/capabilities.h | 4 ++-- arch/x86/kvm/vmx/vmenter.S | 29 +++++++++++++++++++++++++++++ arch/x86/kvm/vmx/vmx.c | 8 -------- arch/x86/kvm/vmx/vmx.h | 4 ++-- arch/x86/kvm/vmx/vmx_ops.h | 2 +- 7 files changed, 42 insertions(+), 15 deletions(-) --- a/arch/x86/kernel/asm-offsets.c +++ b/arch/x86/kernel/asm-offsets.c @@ -18,6 +18,7 @@ #include #include #include +#include "../kvm/vmx/vmx.h" #ifdef CONFIG_XEN #include @@ -90,4 +91,9 @@ static void __used common(void) OFFSET(TSS_sp0, tss_struct, x86_tss.sp0); OFFSET(TSS_sp1, tss_struct, x86_tss.sp1); OFFSET(TSS_sp2, tss_struct, x86_tss.sp2); + + if (IS_ENABLED(CONFIG_KVM_INTEL)) { + BLANK(); + OFFSET(VMX_spec_ctrl, vcpu_vmx, spec_ctrl); + } } --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -196,8 +196,8 @@ void __init check_bugs(void) } /* - * NOTE: For VMX, this function is not called in the vmexit path. - * It uses vmx_spec_ctrl_restore_host() instead. + * NOTE: This function is *only* called for SVM. VMX spec_ctrl handling is + * done in vmenter.S. */ void x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest) --- a/arch/x86/kvm/vmx/capabilities.h +++ b/arch/x86/kvm/vmx/capabilities.h @@ -4,8 +4,8 @@ #include -#include "lapic.h" -#include "x86.h" +#include "../lapic.h" +#include "../x86.h" extern bool __read_mostly enable_vpid; extern bool __read_mostly flexpriority_enabled; --- a/arch/x86/kvm/vmx/vmenter.S +++ b/arch/x86/kvm/vmx/vmenter.S @@ -1,9 +1,11 @@ /* SPDX-License-Identifier: GPL-2.0 */ #include #include +#include #include #include #include +#include #include #include "run_flags.h" @@ -73,6 +75,33 @@ SYM_FUNC_START(__vmx_vcpu_run) lea (%_ASM_SP), %_ASM_ARG2 call vmx_update_host_rsp + ALTERNATIVE "jmp .Lspec_ctrl_done", "", X86_FEATURE_MSR_SPEC_CTRL + + /* + * SPEC_CTRL handling: if the guest's SPEC_CTRL value differs from the + * host's, write the MSR. + * + * IMPORTANT: To avoid RSB underflow attacks and any other nastiness, + * there must not be any returns or indirect branches between this code + * and vmentry. + */ + mov 2*WORD_SIZE(%_ASM_SP), %_ASM_DI + movl VMX_spec_ctrl(%_ASM_DI), %edi + movl PER_CPU_VAR(x86_spec_ctrl_current), %esi + cmp %edi, %esi + je .Lspec_ctrl_done + mov $MSR_IA32_SPEC_CTRL, %ecx + xor %edx, %edx + mov %edi, %eax + wrmsr + +.Lspec_ctrl_done: + + /* + * Since vmentry is serializing on affected CPUs, there's no need for + * an LFENCE to stop speculation from skipping the wrmsr. + */ + /* Load @regs to RAX. */ mov (%_ASM_SP), %_ASM_AX --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6989,14 +6989,6 @@ static fastpath_t vmx_vcpu_run(struct kv kvm_wait_lapic_expire(vcpu); - /* - * If this vCPU has touched SPEC_CTRL, restore the guest's value if - * it's non-zero. Since vmentry is serialising on affected CPUs, there - * is no need to worry about the conditional branch over the wrmsr - * being speculatively taken. - */ - x86_spec_ctrl_set_guest(vmx->spec_ctrl, 0); - /* The actual VMENTER/EXIT is in the .noinstr.text section. */ vmx_vcpu_enter_exit(vcpu, vmx, __vmx_vcpu_run_flags(vmx)); --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -8,11 +8,11 @@ #include #include "capabilities.h" -#include "kvm_cache_regs.h" +#include "../kvm_cache_regs.h" #include "posted_intr.h" #include "vmcs.h" #include "vmx_ops.h" -#include "cpuid.h" +#include "../cpuid.h" #include "run_flags.h" #define MSR_TYPE_R 1 --- a/arch/x86/kvm/vmx/vmx_ops.h +++ b/arch/x86/kvm/vmx/vmx_ops.h @@ -8,7 +8,7 @@ #include "evmcs.h" #include "vmcs.h" -#include "x86.h" +#include "../x86.h" asmlinkage void vmread_error(unsigned long field, bool fault); __attribute__((regparm(0))) void vmread_error_trampoline(unsigned long field,